Graphene/MoS2-Nanoribbons/Graphene Field-Effect Photodetectors: A Numerical Study

We present the results of a numerical study on the characteristics of MoS2-based field-effect photodetectors (FEPhDs). These FEPhDs consist of 12-nm-long and 1.42-nm (1.45-nm)-wide MoS2 armchair (zigzag)-nanoribbons (MoS2-A(Z)NRs), acting as channels connected to two semi-infinite graphene electrodes, serving as source and drain terminals to minimize the terminals' series resistances. The simulation method used here is the nonequilibrium Green's function formalism plus an atomistic tight-binding (TB) model. We employed the TB model to obtain characteristics like the density of states versus electron energy, current–voltage curve, and photocurrent versus photon wavelength (λ). For the latter, we consider illuminating the A(Z)NR channels with a broadband optical signal covering the λ = 330–830 nm range. Our simulations show that passivation of ANR edges with H2 and OH molecules reduces the semiconducting bandgap by ~ 28% (for H-ANR) and ~ 28.6% (for OH-ANR). The numerical results show that, among the three ANR channels, the optimum photoresponsivity of Rph ≈ 43.88 mA μW−1 belongs to the FEPhD with the MoS2-OH-ANR channel biased at VDS = 200 mV and VGS = 0, at λ ≈ 451 nm, independent of the illumination intensity. Among the three ZNR channels, the best photoresponsivity of Rph ~ 27.02 mA μW−1 belongs to the unpassivated channel under the same biasing condition but at λ ≈ 477 nm. The results also show that the optimum biasing condition differs from one FEPhD to another. The results show that the proposed MoS2-A(Z)NR-based FEPhDs can be promising candidates for nanoscale optoelectronic devices in the UV–Vis range.